Magnetic disk devices are widely used as high-speed and high-capacity storage media. These devices employ the logical block addressing (LBA) as a scheme for mapping a linear logical address space to physical sectors of disk media, so that a host can specify the locations of read and write data by using LBA addresses.
Some physical sectors on a magnetic disk may be or may become defective. Upon detection of a defective sector, the magnetic disk device remaps its corresponding LBA address to a different physical sector pooled in a previously secured substitution area. This change in the LBA mapping isolates and hides the defective sector, thereby contributing to an improved reliability of data retention.
See, for example, Japanese Laid-open Patent Publications No. 10-301721 and No. 2004-103127.
It is noted that the substitution area is located away from the physical sectors originally mapped to the logical address space. The foregoing change in the LBA mapping results in a loss of continuity of mapped physical sectors. This means that sequential access to the disk device would no longer be “sequential” in terms of the movement of magnetic heads, and thus the performance of such access would be degraded.